As used herein, high voltage (HV) shall refer to transmission voltages (e.g., between 115 kilovolts (kV) and 750 kV) or voltages on the order of at least 100 kV or more such as 100's of kilovolts, as compared to lower distribution voltages. For example, electric power distribution systems carry electricity from a power generation and transmission system to individual consumers. A power transmission system operates at a significantly higher voltage range than a power distribution system. For example, components in a transmission system operate at voltages ranging between 115 kilovolts (kV) and 750 kV. Distribution substations, on the other hand, connect to the transmission system and lower distribution voltages ranging between 5 kV-69 kV to medium voltages ranging between 2 kV and 35 kV with the use of transformers. Distribution transformers are located near customers' premises. Primary distribution lines carry the medium voltage power to distribution transformers, which further lower the voltage to utilization voltage of household appliance. Accordingly, as used herein, high voltage (HV) shall be understood to refer to transmission voltages (e.g., between 115 kV and 750 kV or voltages on the order of at least 100 kV or more such as 100's of kilovolts), which are typically higher than distribution voltages.
With reference to FIG. 1, a system 10 for measuring high voltages on the order of 100-500 kV, for example, can use a measuring device 12 having a large resistive or capacitive divider 20 to bring down the voltage of the device under test 18 to a lower voltage (e.g., on the order of +/−100 V). An example system is a KVM Series AC/DC kilovoltmeter available from HAEFELY HIPOTRONICS in Brewster, N.Y. having different models with different sizes of dividers 20 for measuring various ranges of voltages such as 0-100 kV, 0-200 kV, 0-300 kV and 0-400 kV. This large divider 20 is then wired to a display circuit 16 via a signal-conditioning board 22 comprising a small divider. In the display circuit 16, the voltage signal is buffered and conditioned using passive components. The display circuit 16 is usually either a meter or a seven segment display, which can show several types of measurements such as, for example, average or root mean square (RMS) voltage (Vrms), +/−peak voltage (Vpp) and AC/DC coupling, by switching mechanically between different analog circuit paths that connect to the display. Two types of selection knobs are provided on these meter heads 16, that is, a knob for AC or DC selection, and a mechanical dial to switch between the respective analog circuit paths for the different measurement types supported by the meter 16.
The line 14 connecting the measuring device 12 with the display device or meter 16 is disadvantageous for a number of reasons. For example, the line 14 provides a conductive connection containing high voltages from the measuring device 12 to the display device 16 where a user will be, thereby exposing the user to an electrical shock hazard since the user's distance from the high voltages is limited by the wire length (e.g., on the order of only 6 meters).
Existing meters for high voltage measurements have different features depending on the particular application. These meters may be used for voltage detection, phase measurement, phase sequence identification, and/or testing for induced or live power lines or equipment. For the testing or calibration of high voltage equipment (e.g., AC/DC Hipot testers and High Voltage DC power supplies), inadequate lighting and distance from the device under test 18 and measuring device 12 to the meter head 16 with display can make reading the numbers on the meter head display very difficult.
The cable connections 14 of voltage probes of conventional high voltage measurement systems present a further inconvenience because such cables 14 make the handling of a measuring device 12, and particularly the handling of plural measuring devices 12 (e.g., such as in a phase measurement test), cumbersome and time consuming. For example, using existing KVM100s for multipoint measurements (e.g., 3-phase power system measurements, or measurements of the primary and secondary sides of a HV transformer) requires a separate instrument and hardwired display at each point of measurement and the associated cabling, which is cumbersome. Further, a user would need to use a HOLD function to capture plural measurements at different points at a particular time, or use cumbersome, custom-made data acquisition equipment hardwired to each device at each test point. Either method presents, however, safety issues in terms of user proximity to the test point and hardwired device.
Accordingly, there is a need for wireless voltage measurement devices and wireless meter heads or other data display devices for voltage measurements (e.g., measurements of voltages peaking in a high voltage range of 100 kV to 500 kV, as well as lower voltages peaking in a medium voltage range of 15 kV to 69 kV), so that voltages can be measured at remote locations and data can be collected and displayed wirelessly and therefore more safely and conveniently without need for cumbersome cabling such as, for example, the illustrative cabling 14 between the measurement device 12 and the meter head with display 16 in FIG. 1. A need also exists for an improved voltage measurement system having wireless measurement devices and a wireless data display device(s) that more conveniently measures, collects and displays voltage measurement data from multiple locations. The improved voltage measurement system can be used with essentially any voltage measurement applications and equipment. Further, examples of high or medium voltage measurement applications and equipment or apparatuses with which the improved voltage measurement system can be used include, but are not limited to, testing motors (e.g., in a hydrocenter) or cables (e.g., in a factory) or transformers that are intended for high or medium voltage operation. Multiple location voltage measurements can be, but are not limited to, three-phase cable testing, testing phase balance or three-voltage measurements on motor terminals, or testing primary and secondary windings of a transformer, for example.